Tehran University of Medical Sciences Basic & Clinical Cancer Research 2228-6527 13 1 2022 01 04 63 71 Elham Ariyabod Department of Physics, Payame Noor University (PNU), P.O.Box 19395-4697,Tehran, Iran. Seyedeh Nasrin Hosseini Motlagh Department of Physics, Shiraz Branch, Islamic Azad University, Shiraz, Iran Saeed Mohammadi Department of Physics, Payame Noor University (PNU), P.O.Box 19395-4697,Tehran, Iran. 2021 04 17 2021 10 10 Background: Beam therapy, the most common and successful treatment used after surgery, plays an important role in treating cancer. In proton therapy, proton beam (PB) particles irradiate the tumor. To enhance the treatment of breast tumors, gold nanoparticles (GNPS) can be injected into the tumor simultaneously as irradiating the PB. Methods: This paper aims to simulate the treatment of breast tumors by using PBs and injecting GNPs with different concentrations simultaneously. We introduced the breast phantom (BP), then we irradiated it with a proton pencil beam, which is also injected with GNPs simultaneously. We used the GEANT4/ GATE7 (G4/G7) code to show the enhancement of the absorbed dose in the tumor. Results: The findings of our simulations show that the location of the Bragg peak within the tumor shifts to higher depths with increasing energy. Also, by injecting GNPs in different amounts of 10, 25, 50, and 75 mg/ml with simultaneous irradiation of the PB, the rate of absorbed dose increases up to 1.75% compared to the non-injected state. Our results also show that the optimal range of proton energy that creates the Bragg peaks within the tumor is between 28 to 35 MeV, which causes the spread out of the Bragg peak. It should be noted that the amount of absorbed dose is affected by quantities such as total stopping power, average Coulomb scattering angle, CSDA range, and straggling range. Conclusion: This work offers new insights based on the use of GNPS in the treatment of breast cancer through proton therapy and indicates that adding GNPS is a promising strategy to increase the killing of cancer cells while irradiating fast PBs.In fact, the results of this study confirm the ability of GNPs to enhance treatment by increasing the absorbed dose in breast tumors using proton therapy. https://bccr.tums.ac.ir/index.php/bccrj/article/view/381 https://bccr.tums.ac.ir/index.php/bccrj/article/download/381/480